This invention is related to an electrically conductive coating and in particular an electrically conductive coating that does not contain carbon black pigment.
Primers and conductive primers are well known in the art and are used in the manufacture of automobiles and trucks. Tremper U.S. Pat. No. 4,470,426, issued Apr, 26, 1988 shows a conductive primer composition. Also, conductive guide coats or primer surfacers used over plastic parts are known and are shown in Tremper U.S. Pat. No. 4,470,566, issued on Apr. 26, 1988.
In modern auto and truck manufacturing facilities, the topcoat of paint is applied by electrostatic spraying which reduces paint losses and air pollution caused by paint over-spraying. Electrostatic spraying substantially reduces over-spraying since the electrostatic charge on the atomized paint particles results in most of the paint being deposited on the substrate. However, to efficiently electrostatically spray paint, the substrate must be electrically conductive and the substrate must be grounded. After a primer has been applied by either spraying, dipping, or electrocoating to a steel metal autobody substrate such as a fender, door, or hood, the metal part is insulated by the primer making it difficult to ground or if the substrate is plastic the substrate is not electrically conductive and cannot be grounded. The aforementioned conductive primers, guide coats or primer surfacers can be applied to achieve the necessary level of conductivity to make the substrate conductive and allow the substrate to be grounded for effective electrostatic spraying. However, to achieve the needed level of conductivity, a conductive carbon black pigment or black iron oxide is used which gives the composition a dark color which requires the use of a thicker layer of topcoat to cover the darker color of the primer, guide coat or primer surfacer. There is a need to eliminate the black pigment and replace it with a conductive pigment system which would eliminate the color problem and allow for the use of normal topcoat thickness of paint. The use of less paint would reduce manufacturing cost and reduce air pollution problems.